The use of a sequence of reference calibration patches exposed on a roll of film to enable better exposure control during optical printing is known in the art. See for example U.S. Pat. No. 5,767,983 issued Jun. 16, 1998 to Terashita entitled Color Copying Apparatus for Determining Exposure Amount from Image Data of an Original Image and a Reference Image. The use of calibration patches has also been shown to be useful in determining correction values for scanned film data used in digital printing. See for example U.S. Pat. No. 5,667,944 issued Sep. 16, 1997 to Reem et al. entitled Digital Process Sensitivity Correction; and U.S. Pat. No. 5,649,260, issued Jul. 15, 1997 to Wheeler et al. entitled Automated Photofinishing Apparatus. It is also known to provide barcode data relating to film type and frame number on the edge of film for use in photofinishing.
The reference calibration patches used in these calibration procedures can be neutral, colored or any combination thereof. The neutral patches are created by using approximately equal red, green, and blue actinic exposures. Unfortunately, exposures which produce reference calibration patches that are of low contrast with respect to their background, such as obtained upon development of isolated low exposure areas on a color negative film, are difficult to locate with adequate accuracy in a digital image.
Depending on the application, many scanner types are used in the industry to obtain digital images. A scanner can employ a point sensor to acquire data one pixel at a time from a single, usually small, region of an image at one time and accumulate a full image by two-dimensional relative motion between the sensor and image. A scanner can employ a line array sensor to obtain a full line of pixels at a time and accumulate a two dimensional image by one dimensional relative motion between the sensor and image. A scanner can employ an area array detector and directly acquire a two dimensional image. The transport mechanism to feed a photographic element into a scanner can be one or more of many types, including a manual thrusting or positioning mechanism, a cartridge thrust mechanism, or a high speed continuous feed mechanism. Each class of scanner sensor and transport mechanism can introduce variation in the location and geometry of a digital image relative to the physical image due to variations in alignment, magnification, transport velocity, etc. All these variations make location of patches more difficult.
One solution to the problems of locating reference calibration patches is to additionally print easily identifiable and locatable features onto the photographic element, also called fiducial marks. See U.S. Pat. No. 5,198,907 issued Mar. 30, 1993 to Walker et al. entitled Method and Apparatus for Automatically Locating Predefined Exposure Areas in a Scanned Image which discloses printing an L shaped registration mark having defined lengths relative to an exposure area in a scanner calibration original. The problem with printing such fiducial marks is that they require exposure apparatus and occupy valuable area on the photographic element, area that would preferably be used for additional reference sensitometric patches or other data.
A need remains to provide an improved method for locating sensitometric patches on photographic elements.